Intracellular misfolding or misprocessing of proteins is a critical problem in numerous human diseases including neurodegenerative disorders, diabetes and cancer. The ability to specifically target and manipulate individual protein variants in situ would be a powerful tool in treating these diseases. Inhibitory RNA techniques have revolutionized cell studies, providing the ability to selectively inhibit expression of single genes. Many diseases and cellular processes however result from aberrant protein folding or processing, or from formation of protein complexes, events which cannot be controlled by RNAi. A powerful complementary approach to RNAi techniques would be the ability to selectively target and manipulate a misfolded, misprocessed or complexed protein form intracellularly. In this proposal we will develop reagents that can bind specific protein variants using robust intracellular protein frameworks. Different tags can be added to target specific cell locations and pathways including proteasomes and lysosomes for protein degradation, endosomal targeting for cell internalization, and cell secretion for protein removal. A variety of very exciting applications can be addressed including: 1) targeting misfolded and misprocessed proteins involved in human health problems including neurodegenerative diseases, diabetes and cancer, 2) targeting cell signaling pathways to control apoptosis in diseased cells or differentiation in stem cells, 3) developing chaperone-like reagents that can promote correct protein folding in situ, and 4) targeting viral proteins involved in replication or assembly to provide a means to control viral infection especially in brain tissue. The overall goal of this project is to develop reagents that can be readily modified to intracellularly bind a selected target protein variant and manipulate that target in a predictable manner to achieve a desired result. This ability to manipulate specific intracellular targets can have profound impact on numerous health problems.